Hi, before buying I would like to ask about multiplayer option for GoG release. Is there LAN support or do I have to create some sort of online account or is there any sort of online DRM?

Answered by berzebub3.14 (one of the devs) on Steam forum:
"There is no DRM and there is cross play with gog. If you want play online game you need to have internet access but you do not create any account."

EDIT: and from A'vee (one of the devs too):
"As long as you use the same version (see build number) - everything should be fine."

This should be mentioned as well: you should also have the same event modules.